


Five Blue Tongues

by yastaghr



Series: Underswap #832 [3]
Category: Undertale (Video Game)
Genre: Alpha/Beta/Omega Dynamics, Alternate Universe - Errortale (Undertale), Alternate Universe - Underswap (Undertale), Bondage, Breeding, Claiming Bites, Come Inflation, Ecto-Penis (Undertale), Ecto-Tongue (Undertale), Ecto-Vagina (Undertale), Enthusiastic Consent, Error Sans - Freeform, ErrorBerry - Freeform, Gags, Implied/Referenced Abuse, Implied/Referenced Domestic Violence, Knotting, M/M, Mating Bites, Mating Cycles/In Heat, Penis In Vagina Sex, Porn With Plot, Porn with Feelings, Prostitution, Rough Sex, Sanscest - Freeform, Shibari, Smut, Underswap Sans (Undertale)
Language: English
Status: Completed
Published: 2020-04-24
Updated: 2020-04-24
Packaged: 2021-03-01 17:56:20
Rating: Explicit
Warnings: No Archive Warnings Apply
Chapters: 1
Words: 3,734
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/23821192
Author URL: https://archiveofourown.org/users/yastaghr/pseuds/yastaghr
Summary: Blue and Error are just good friends. But can one little encounter change that forever?
Relationships: Errorberry, Sans/Sans (Undertale)
Series: Underswap #832 [3]
Series URL: https://archiveofourown.org/series/1933717
Comments: 24
Kudos: 254
Collections: Glitchy Boi is Best Boi





	Five Blue Tongues

A dark-wood doorway rippled into view in the white monstrosity that was the Anti-Void. Well, it had once been white. It was now filled with furniture, boxes of craft supplies, and stolen food. The ceiling was dripping with glimmering blue threads that looked like the most disorganized spider web on the planet. Human and monster souls of a thousand different colors were scattered in the ropes. Against all that, a dark brown stained wooden door that suddenly appeared was hardly out of place. It would have made more sense if it had come with a wall, though. Or if it touched the floor. Instead it hovered about half a meter above the ground.

The doorknob rattled for a moment, then it fell off. Someone on the other side of the door cursed. It was a high pitched voice, and the way it swallowed the tail of the word implied that it might get in trouble for swearing. Nothing but dread-filled silence happened for a moment, then a knocking started. It was persistent, incessant, and arrhythmic. In other words, it was designed to annoy whoever was on the other side of it into opening the door.

After about ten seconds of this an irritated voice cursed it’s way over to the door, occasionally crashing into things and breaking them. This voice was glitched and smokey. It belonged to a multi-colored skeleton, mostly black with bits of red and yellow, who was wearing a paint-spattered t-shirt and gym shorts. He had a ball of steel wool in his hand. His skull was still half-covered in bubbling green paint. The other half was covered in soap that smelled like lemons.

“dAmNiT, bLuE, wHy dOn't yOu jUsT OpEn tHe dOoR? i gAvE YoU ThE KeY To...oH,” Error took in the state of the knob on the floor. “dAmN. i wOnDeR WhAt fReAk gAvE StReTcH ThIs iDeA. sToP YoUr hAmMeRiNg, BlUe, I NeEd tO OpEn yOu a pOrTaL.”

Error took a step back and opened a glitchy portal into Underswap #832. Blue was standing with his back to him, facing the door to his room that, unfortunately, still had the backside of the lock panel but no longer had a doorknob. Blue spun on his heels (actual heels, Error noticed. A simple pair of red pumps). The skirt of his 60s style halter dress spun out. Error couldn’t make out the pattern without his glasses, but it looked vaguely red on white. Both were good colors against Blue’s, well, blue magic. There seemed to be a lot of it showing today.

Blue ran through the portal and crashed on a nearby couch, panting. Error closed the portal, dismissed the door, and turned to face his friend. He looked nice, as far as Error understood the matter. Why was he wearing all that when he was just coming here? Error crossed his arms and tapped his foot, waiting to find out.

Blue gave him a sheepish smile and said, “Hi, Error. Thanks for rescuing me. Stretch is getting even more...well, he didn’t like that I was going out to a public dance with Alphys and Undyne dressed like this, so he locked me in my room. I texted Alph only to find out he’d called telling her I tripped coming down the stairs and broke both my legs, so I know what’s coming later, at least. I didn’t realize he’d decided to mess with the doorknob. He’s never done that before.”

“yOuR BrOtHeR Is aN AbSoLuTe fUcKeR. aRe yOu sErIoUsLy gOiNg tO LeT HiM BrEaK YoUr lEgS JuSt tO KeEp uP ApPeArAnCeS?” Error growled. 

He hated Stretch, like, a lot. But Blue had made him promise not to kill him. He’d said something about it being a problem with Stretch’s soul that he’d fix as soon as they got to the Surface and he made it through medical school and got his MD that way. Stretch had to agree if it came from a doctor, right? Error didn’t believe it for a minute, but a promise was a promise, and, anyway, it was the only way he could convince Blue not to try and lecture Ink for hurting him so much. Ink would probably turn on him like he turned on Dream after he announced that Nightmare and he were going to soul bond and raise kids. That had gone horribly. Error didn’t want the same thing for Blue. Dream was a god. He could survive wounds that would kill Blue. No backtalk at Ink.

Blue looked down. “Well, you said Chara wasn’t going to leave the Ruins this round, so I just need to keep things going until they RESET. I don’t know how long it will be until they get bored. So I have to.”

Error grumbled, “yOu wOuLdN'T If yOu'd jUsT LeT Me tAkE SoMe dUsT FrOm aNoThEr uNdErSwAp sAnS AnD LeAvE It iN YoUr rOoM WiTh a nOtE. iT'S NoT LiKe hE WoUlDn't bE HaPpY FoR YoU To gO.” The way Blue talked about it, everyone would.

Blue sighed. “I don’t know, Error, I just...I don’t want to do that to Chara. They’re a nice kid, and they need me to get to the Surface.”

“tHaT WoUlDn't bE A PrObLeM If yOu'd jUsT LeT Me tAkE ThEiR SoUl sO YoUr wOrLd fReEzEs aGaIn. No oNe bUt yOu aNd tHeM WoUlD KnOw.”

Blue huffed. “Error, drop it. I’m not doing it and that’s final. Now, how did your-”

The whole Anti-Void convulsed with a red aura. Error and Blue both flinched.

“rEaLlY, aNoThEr oNe? FuCkInG HeLl, InK, jUsT LeT Up fOr fIvE MiNuTeS, wOuLd yA? hEh. SoRrY BlUe. YoU KnOw hOw iT Is. I'Ll bE BaCk iN No tImE. lItErAlLy. HeH.”

Blue waved a bandaged hand at him. “No, no, go ahead. Try not to let Ink hurt you, but if he does, I brought my medical kit. Have fun!”

Error’s eyes gleamed. “oH, i wIlL. tHiS TiMe iT'S An uNdErSwAp. I CaN TeAr sTrEtCh aPaRt aLl i wAnT AnD StIlL KeEp mY PrOmIsE. hEh. If oNlY I CoUlD Do iT To tHe rEaL OnE.”

“Error,” Blue said warningly.

Error opened a portal to the new Underswap copy Ink had made and waved Blue away. “i kNoW. sEe yOu wHeN I GeT BaCk.” Then he stepped through the portal and left Blue to his own devices.

* * *

The first sign that Error had returned was a low growl that shook the souls in their web. The next thing was a smoky scent, the kind of smell that comes off a burned out computer. Underneath that was a musky smell that had Blue sitting bolt upright in his chair, blushing. Was Error going into rut? Maybe he should leave...no, first he should make sure that Error had someone to help, then he could leave. He knew how hellish it was to suffer through a heat alone. A rut probably felt similar for an Alpha.

“Error! I’m in the knitting room!”

Thumping and grumbling followed a convoluted path. Finally Error walked through the nonexistent wall from the kitchen and flopped into the other chair. He had more paint all over him, and one of his arms looked like it had gotten splashed with acid. Blue immediately pulled out his medical kit and started tending to it. He let some small talk float between them.

“So, Error, I didn’t realize you were an Alpha. That’s a lovely scent you have there. Who are you going to share your rut with? One of Nightmare’s gang?”

Error looked at him with a deadpan that just barely hid confusion. “yEaH, nO, i'm nOt gOiNg iNtO RuT. i'm nOt dUe fOr aNoThEr...tWo wEeKs? SoMeThInG LiKe tHaT. sO YoU DoN'T HaVe tO FuCk oFf aNd wE CaN JuSt gO BaCk tO KnItTiNg iN PeAcE.”

Blue secured the end of the bandage he’d been wrapping and stood up, right in Error’s personal space, but still conscious enough not to touch him. He could already feel his resonant heat starting. Error’s smell was strong, and Blue’s heats could be set off so easily after all the monsters he’d been with. Time to use that to his advantage.

“Error, take a whiff of my scent and tell me what you feel.”

Error reflexively sniffed. His face focused and blushed with yellow heat. He panted, “iT SmElLs sO FuCkInG GoOd, BlUe, I-” He teleported a few feet away. His face was a ticked off scowl. “nO, yOu'rE TrIcKiNg mE. sToP It.”

Blue calmly sat down on the start white “floor” of the Anti-Void and spread his legs open obscenely wide. “There’s no trick here, Error. I resonate with just about everyone, so your rut kicked off my heat. If you want me to leave, I will, but I am completely available for you to use to get over your rut.”

Error laughed giddily and wiped a hand across his face. “hEh. YoU'Re jUsT MaKiNg iT Up. YoUr dAyS As a pRoStItUtE ArE CoMiNg bAcK AnD YoU JuSt wAnTs tO FuCk tHe oNe pErSoN WhO DoEsN’T HaTe yOu.”

Blue winced. That one hit a little bit too close to home. Reluctantly, he said, “You’re probably right. My heats have been unbearable because no one would help me with them. This is the first time there’s even been a chance. :But I said you were free to kick me out. I wish you luck finding someone you actually want who will help you through this rut.”

Blue brought his legs together and attempted to push himself to his feet. Familiar blue strings wrapped around him and bound him in place, leaving only his hands free to move. Blue watched Error stomp over to him. He set his hands on his hips and loomed over Blue.

“tHaT’S NoT WhAt i mEaNt aNd yOu kNoW It, BlUe,” Error barked at him.

Blue gulped, swallowed his excitement, and asked, “What did you mean, then?”

The yellow blush on Error’s cheeks was quite lovely. The glitched stammering was, too. It sounded almost like a song. Finally, Error strung together his words. “sHuT uP!”

Cheeky giggles escaped Blue’s mouth. “You should make me, Error.”

Error growled and pushed him back with a slipper-clad foot. Blue went down willingly, opening his legs wide and inviting Error to have his way with him. “I can still speak, you know.”

Blue strings snaked around his skull and bound his mouth wide open. It hurt a bit at first, but his body got used to the stretch and calmed down. Error did not. He summoned a sharp bone and carefully sliced his way through Blue’s dress. Too bad. He loved this little rose-covered halter dress, but letting Error be in control was more important. Error needed this. He was an Alpha; Blue was an Omega. That was all that needed to be said. 

* * *

Error raked his eyes over Blue’s many scars. His eye lights lingered on his lowest left rib, which was still over calloused after being broken. His hand reached over to touch it, but froze a millimeter away. He just couldn’t bring himself to touch Blue. Even though it was Blue, his haphephobia was still too strong. This was going to be a problem. Error glared at him, willing himself to come up with a solution. Finally, he had one. He’d never had a problem touching someone’s magic before. If Blue just summoned enough magic, Error wouldn’t have a problem touching him.

“sUmMoN ThAt wEiRd tHiNg wHeRe yOu wRaP MaGiC ArOuNd aLl yOuR BoNeS,” Error ordered him. Blue complied. A thin ecto-body came into existence with a sound like ‘gloop’. It started at his collarbone and extended down to his ankles and wrists. It was pretty light blue, almost a periwinkle color. There weren’t any visible scars, but Error knew better than to trust that. He wanted to see the real Blue. “nO, nOt tHaT OnE, tHe rEaL OnE. i kNoW YoUr bRoThEr hAs gIvEn yOu sCaRs. ShOw tHeM To mE.”

This time the ecto-body Blue showed him was almost tragically thin. There were scars everywhere. A few were even fresh, not bleeding but not healed. There was a giant slash that cut between his plump breasts that Error knew every Sans had. Most of the rest, the newest ones anyway, were from Stretch. 

Error reached out and touched one of those scars, a circle-shaped divot a few centimeters across that lay just above Blue’s iliac crest. It was pitted, but Error loved the texture on it almost as much as he loved getting to touch his best friend. He explored the feel of it, then another, then another. Before long he had touched every scar on Blue’s body, and he loved them all. Blue had never shown them to anyone but him. That made them his. 

Blue wriggled underneath him and Error smiled. His strings held Blue down with just enough force to let him wiggle like a worm, but not get away. Speaking of strings, he felt like adding a couple more. He pulled a few strands out of his eye and quickly wove them into a rope. He made a loop halfway through it, tied the loop off, and pulled the tails on either side of Blue’s neck. Then he made what looked like a chain ladder down the front of Blue’s body, ending with the tails separated on either side of his crotch. 

Then Error slipped the tails underneath Blue without crossing them and fed them through the loop he had made at the beginning. He then made a very pretty double zigzag that attached to either side of the rope ladder and pulled it tight across Blue’s chest. He finished the ropes off just below Blue’s butt, which was loose and jiggly. 

The sight of Blue wrapped up prettily in all his strings made Error horny as hell. He slipped the thumb of his right hand under the hem of his shorts and revealed his dick. It was the classic short, thick shape of every Sans dick done up in neon blue. There were several uneven ridges along the length of it, almost like error bars. Beneath them was a thick, thick knot. All in all it was an intimidating dick that made Blue salivate. 

“hEh. SeE SoMeThInG YoU LiKe tHeRe, BlUe? DoN'T BoThEr aNsWeRiNg. YoU'Re lUcKy i'm iN RuT RiGhT NoW, oThErWiSe i'd nEvEr sToOp sO LoW As tO ToUcH YoU. nOw, SuMmOn a dEcEnTlY BiG PuSsY FoR Me. DoN'T FoRgEt tO AdD A WoMb. I ThInK YoU'D LoOk gOrGeOuS AlL KnOcKeD Up wItH A LiTtEr fOr mE,” Error chuckled evilly. 

The pussy Blue summoned was better than Error could have imagined. There was a big clit throbbing for him, and blue slick pooling on the white floor of the Anti-void. The lips were puffy, and he could see the shape of Blue’s whole reproductive tract through the glow of his magic.

Error growled through his smile, “i kNeW YoU'D Be eAgEr tO Do tHiS. i cAn't wAiT To fEeL YoU ArOuNd mE.”

He started rubbing his dick in Blue's juices. It wasn't anywhere near the strong, confident strokes he had intended. There were way too many glitches for that, and he just couldn't bring himself to thrust too hard against Blue. He knew how fragile his best friend was, and he really didn't want to see what his dust looked like. It was bad enough that he had to kill other versions of Blue. He didn't want to kill this one. 

When those first few strokes didn't hurt Blue, Error grew more confident. Soon he was rutting into Blue like a rabbit. 

Error's growls turned into panting. The look in Blue's eyes made him impatient. It was drawing him in, willing him to fuck him now. Who was Error to argue with that? “I cAn’T fUcKiNg WaIt AnYmOrE!” Error warned Blue. Then he hilted inside of Blue’s pussy in one quick move. He didn’t wait long before setting a rough place. Blue’s boobs jiggled like jello in an earthquake. 

The fast, hard pace had Blue moaning around the gag in his mouth. His lovely, sweet scent was driving Error mad. No wonder he’d been so successful as a prostitute in his world. Error would have paid good money to get to have his way with an Omega that smelled this good. He didn’t understand how people could just abandon him. He was scrumptious, but he was also smart, kind, and absolutely devoted to the people he loved. Why didn’t someone snatch him up like the perfect little mate he was?

Error growled as his impossible pace sped up. “yOu’rE So fUcKiNg tEmPtInG, bLuE. i nEvEr tHoUgHt i’d gEt tO FuCk yOu. YoU’Re sO FuCkInG TiGhT It’s uNbElIeVaBlE. sO SoFt, ToO. yOu fEeL So gOoD AgAiNsT My rIdGeS. i hOpE ThEy fEeL JuSt aS GoOd tO YoU.”

Blue nodded as much as he possibly could around the restraining and gagging strings. Error’s insane grin widened. “gOoD. i cAn’t wAiT To fIlL YoU To tHe bRiM. i wOnDeR HoW MuCh i cAn mAkE YoU SwElL WiTh mY CuM. yOu’rE LiTtLe bElLy wOuLd lOoK So nIcE RoUnDeD OuT WiTh mY MaGiC. hEh. It wOuLd lOoK EvEn bEtTeR RoUnDeD OuT WiTh mY BaBiEs iN YoUr bElLy. I WoNdEr hOw mAnY I CaN PuT In? NiGhTmArE’S BeEn aNnOyInG Me wItH HoW MuCh hE BrAgS AbOuT DrEaM’S BiG LiTtEr. YoU’D BeTtEr gIvE Me mOrE BaBiEs tHaN ThAt pAlTrY NuMbEr. We’lL NeEd aT LeAsT SiX, bUt i kNoW YoU’Ll bE A PeRfEcT PaReNt fOr tHeM. iF YoU CaN TaKe cArE Of tHaT FuCkInG BaStArD Of a bRoThEr yOu cAn tAkE CaRe oF AnYtHiNg.”

The eye lights in Blue’s sockets had widened the moment Error’s monologue had turned to breeding, but Error could see the eagerness in his face. If that wasn’t enough, Blue was nodding almost desperately. Nothing could up a monster’s confidence like that kind of consent.

Error let his thoughts wander into some fantasies that he’d been harboring for a long, long time while he pounded into Blue’s tight cunt. “i wOnDeR WhAt iT WoUlD Be lIkE? i’d cOmE HoMe fRoM ThE EnD Of a lOnG DaY DeStRoYiNg aUs tO FiNd yOu aLrEaDy wAiTiNg iN ThE AnTi-vOiD FoR Me, SaFe AnD sOuNd. YoU’D Be eAgEr tO TeNd mY WoUnDs lIkE AlWaYs, BuT NoW It wOuLd bE JuSt a bIt oF A ChAlLeNgE. hAvInG ThE BaBiEs gRoWiNg iN YoUr bElLy wOuLd mAkE BeNdInG So mUcH HaRdEr. YoU’D LoOk aBsOlUtElY GoRgEoUs lIkE ThAt.”

Error was close, but he didn’t notice. He was too wrapped up in his fantasy. “tHeN I WoUlD PuLl yOu cLoSe aNd iT WoUlDn’t hUrT BeCaUsE YoU’Re mY MaTe. I’D GeT To hUg yOu aNd kIsS YoU… oH, fUcK, bLuE!”

He buried himself inside of Blue, then pushed his knot inside Blue’s pussy with a pop. He rocked excitedly into Blue as the balloon of his womb expanded and expanded, filling up with Error’s cum. His grin expanded, too. Five blue tongues licked his lip as he watched himself cumming. Then he threw all caution to the wind and pressed his lips to Blue’s own. It… didn’t hurt? He was touching teeth to teeth and bone to bone, and it wasn’t hurting! Did that mean-

Error pulled back to look into Blue’s eyes and saw the naked desire in his face. Then he watched as Blue deliberately bent his head to one side, exposing his neck in a very plain show of raw submission. Blue wanted him. Blue  _ wanted _ him. 

He growled and dug his teeth into Blue’s shoulder. The blood and raw magic on his tongues was amazing. He poured in his own magic, marking Blue as his for the rest of their shared lives.

Error didn’t bother to release his grip when he felt his knot give out. He just shifted his hips, pulled his dick out of Blue, released the strings that held Blue to the ground and the ones that gagged him, and wrapped himself around Blue in their place. If he was going to get to touch Blue without it hurting he was going to take full advantage. Besides, being close would strengthen their bond. They had the rest of his rut to spend together. Error wasn’t going to waste a second of it.

* * *

Blue felt like he was on cloud nine. Error’s magic was rushing through him, not just in his uterus but in his blood now, too. He’d claimed him. He’d actually  _ claimed _ him. He wanted to laugh, but he also wanted to cry. He’d wanted this for so long, but he’d never thought it would be Error. But those words had sparked a desire in him that was even stronger than he’d ever imagined. He was so, so glad to be Error’s.

Still, it was probably a good idea if they talked about this some more. Communication was essential in a healthy relationship. “Error,” There was no response, “ _ Error _ ,” Blue said, putting just a bit more force into the words.

Error prized himself off of Blue and shot a glare at him. The glare held no real ire whatsoever. “wHaT?”

He hesitated. What was it that he wanted to say? He let the first thing that popped into his mind pass his lips. “You felt comfortable and in control, right Error?”

The black-boned skeleton laughed. “i wAsN’T ThE OnE WhO WaS TiEd uP AnD GaGgEd, BlUe,” Error said. Blue gave him a look. It was the one that said, ‘this is important to me, so please answer my question’. Error grudgingly admitted, “iT wAs FiNe.”

Blue smiled and rested his head against Error’s shoulder. “I’m glad. Um…” Blue hesitated, but the feeling in his stomach pushed him on, “... Did you mean what you said about me carrying your children? I know you just claimed me, and that makes us mates now, but I don’t want to assume that you really meant that.”

Error looked down at him as if he was mad. “oF CoUrSe i mEaNt iT.”

“That’s good, then, because… I can kind of already feel the souls developing inside of me? I can’t tell how many there are, but the little sparks are there. Is… that okay, Error? Error?”

Blue looked up at him, then giggled. The loading bar hovering above them told him everything he needed to know. Blue shifted just a little, finding a comfortable position to wait in. He was looking forward to seeing Error every day, too.

**Author's Note:**

> You can find me on:
> 
> Pillowfort - https://www.pillowfort.social/Yastaghr  
> Tumblr - https://yastaghr.tumblr.com  
> Twitter - https://twitter.com/yastaghr


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